This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A064692 #21 May 22 2025 10:21:34
%S A064692 1,0,0,0,1,0,1,0,2,1,1,0,0,0,1,0,1,0,2,1,1,0,0,0,1,0,1,0,2,1,1,0,0,0,
%T A064692 1,0,1,0,2,1,2,1,1,1,2,1,2,1,3,2,1,0,0,0,1,0,1,0,2,1,2,1,1,1,2,1,2,1,
%U A064692 3,2,1,0,0,0,1,0,1,0,2,1,3,2,2,2,3,2,3,2,4,3,2,1,1,1,2,1,2,1,3,2,2,1,1,1,2
%N A064692 Total number of holes in decimal expansion of the number n, assuming 4 has 1 hole.
%H A064692 Indranil Ghosh, <a href="/A064692/b064692.txt">Table of n, a(n) for n = 0..50000</a>
%F A064692 a(A001742(n)) = 0. - _Michel Marcus_, Jul 25 2015
%e A064692 We assume decimal digits 1,2,3,5,7 have no hole; 0,4,6,9 have one hole each; 8 has two holes. So a(148)=3.
%t A064692 Table[DigitCount[x].{0, 0, 0, 1, 0, 1, 0, 2, 1, 1}, {x, 0, 104}] (* _Zak Seidov_, Jul 25 2015 *)
%o A064692 (Python)
%o A064692 def A064692(n):
%o A064692 x=str(n)
%o A064692 return x.count("0")+x.count("4")+x.count("6")+x.count("8")*2+x.count("9") # _Indranil Ghosh_, Feb 02 2017
%Y A064692 Cf. A001742, A064532, A064693, A206439, A064692, A208568.
%K A064692 base,easy,nonn
%O A064692 0,9
%A A064692 _Matthew Conroy_, Oct 11 2001